Neurological effects of parasitic infection in dogs and cats

Pet owners are often unaware of the potential dangers that parasites pose. Among the most dangerous are those that can cause neurological damage. Parasitic infection in dogs and cats can lead to serious health problems, including damage to the nervous system, which manifests in a wide range of signs.

Where can a dog or cat pick up parasites?

Dogs and cats can become infected with parasites in many ways, mainly through contact with a contaminated environment. This most often happens during walks in parks or on beaches, where animals may eat contaminated soil or grass. It is important for owners to clean up after their pets regularly to minimise the risk of infection, because the presence of other animals’ faeces increases the likelihood of parasites in the surroundings. In addition, cats, especially those that spend time outdoors, may come into contact with infected rodents or birds, which also exposes them to infection. Regular cleaning and keeping an eye on the environment are key to our pets’ health.

The most dangerous parasites: routes of infection and signs

Toxocara canis, the dog roundworm, and Toxocara cati, the cat roundworm

Toxocara canis is an intestinal parasite belonging to the nematode family and is most commonly found in dogs. The adult worms live in the animal’s intestines, where they lay eggs that are passed in the faeces. These eggs can survive in the environment for a long time, acting as a source of infection for other dogs and, in particular, for puppies.

How does infection occur?

Infection can occur as early as in the womb, via the transplacental route (mainly in dogs), and after birth through the mother’s milk (dogs and cats). Most often, however, animals become infected by ingesting eggs present in a contaminated environment, for example in soil, sand or on grass, where the faeces of infected dogs can remain for a long time. 

The time from ingestion of the eggs to the development of larvae is usually 2 to 4 weeks, depending on the parasite species and environmental conditions. In the case of the dog roundworm (Toxocara canis), swallowed eggs can develop into larvae within the host’s body in around 2–3 weeks. For the cat roundworm (Toxocara cati) this can take up to 4–8 weeks.

What signs appear after parasitic infection in dogs and cats?

The signs of toxocariasis may include seizures, balance problems, weakness and behavioural changes, which point to the parasite’s effect on the nervous system. Veterinarians  may recommend diagnostic tests, including faecal examination, to confirm the presence of parasites. Treatment usually involves antiparasitic medication that eliminates Toxocara from the body. If neurological signs are present, the vet may also prescribe supportive medication, such as anticonvulsants, to minimise the effects of nervous system damage and restore the animal to health.

Neospora caninum

How does infection occur?

Neospora caninum is a parasite belonging to the protozoa. It is mainly responsible for disease in dogs, particularly puppies, and is also a significant problem on farms, where it causes disease in cattle. 

Infection most often occurs through eating meat containing the parasite, but it can also be passed across the placenta or through the mother’s milk. Although neosporosis can occur in animals of any age, most cases are recorded in puppies aged 3 to 5 weeks, in whom the disease runs a fairly acute course. In older dogs neosporosis takes a chronic form.

What signs appear after infection?

Initially the disease is asymptomatic. The prepatent period lasts up to 2 weeks, during which the protozoa multiply mainly in the lungs, liver, pancreas, heart muscle and spinal cord. Only once the parasite has matured and inflammation of the nerves and muscles, along with tissue necrosis, has set in do noticeable signs appear.

In puppies the signs may include paresis or paralysis of the hind limbs, which may spread to the front legs, extensive muscle wasting and stiffness of the limbs, which restricts the pet’s mobility. Puppies may also have difficulty swallowing, diarrhoea and breathing difficulties.

In adult dogs possible signs include altered consciousness, hypermetria, ataxia, intention tremor, cranial nerve deficits, unequal pupils, limb paresis, neck pain and epileptic seizures.

Dirofilaria immitis

How does infection occur?

Dirofilaria immitis, known as heartworm, is a parasite that mainly infects dogs but also cats, although it is less common in the latter. Infection occurs mainly through the bites of infected mosquitoes, which act as intermediate hosts and introduce the parasite’s larvae into the animal’s bloodstream. After infection, the larvae migrate to the heart and large blood vessels, where they develop over 6–9 months into adult worms.

What signs appear after infection?

After infection with Dirofilaria immitis, the signs in animals can vary and develop depending on the severity of the infection and how long the parasite has been established in the body. Although most signs centre on the cardiovascular system, significant neurological signs can also occur, such as:

1. Seizures, resulting from brain damage or an inadequate blood supply to the brain caused by the presence of the parasites.
2.  The infection can lead to problems with coordination, resulting in falls or difficulty moving. Animals may show weakness in the hind or front limbs, which in turn affects their ability to carry out everyday activities.
3. Some dogs may become apathetic, less active or show signs of disorientation, which may suggest damage to the nervous system.

Preventing parasitic infections in dogs and cats

Preventing parasitic infections is a key part of looking after the health of our four-legged friends. Appropriate preventive measures help not only to eliminate existing parasites but also to protect against future infection. 

1. Using antiparasitic products: a wide range of products is available, such as spot-on drops, tablets and collars, which protect against both common and less common parasites such as fleas, ticks and nematodes. They should be used as recommended by your vet and tailored to your animal’s individual needs.
2. Environmental control: cleaning up after your pet on walks is a key element in preventing infection with parasites such as Toxocara, which develop in faeces. Regularly tidying the garden and keeping an eye on the surroundings will help minimise the risk of parasites in your pet’s immediate environment.
3. Avoid contact with wild animals: dogs and cats should have limited contact with wild animals, which may carry various parasites. 
4. Hygiene: keeping the areas where animals spend time clean is important in preventing the spread of parasites. Regularly washing beds, toys and pet accessories will help reduce the risk of infection.
5. Regular veterinary visits: routine visits to the vet, including faecal check-ups and advice on prevention, allow your pet’s health to be monitored on an ongoing basis and any problems, including parasitic infections, to be detected early.

Summary

Parasitic infections such as Toxocara canis, Neospora caninum and Dirofilaria immitis can lead to serious health problems in dogs and cats, including neurological signs. At our Zviropolis Veterinary Clinic we have neurology specialists who can help diagnose parasite-related health problems and put the right treatment in place. Remember that by looking after our pets’ health we also protect ourselves from possible infection. Prevention and good health care are the key to a long, happy life for our animals, and to our own peace of mind and safety.